The present invention relates to an absorbent structure consisting of an absorbent material layer and an airlaid material layer, and to a method for producing an absorbent structure which is intended for use in an absorbent article, such as a sanitary towel, panty liner, incontinence pad, diaper, bandage, saliva absorber, or the like.
Absorbent articles of this type are known in a large number of designs. The absorption body in these products can be produced by means of cellulose pulp, for example in rolls, bales or sheets, being dry-defibered and converted in fluffed form to a pulp mat, sometimes with admixture of so-called superabsorbents, which are polymers having the ability to absorb several times their own weight of water or bodily fluid.
The pulp body is often compressed, on the one hand in order to increase its ability to spread liquid, and on the other hand to reduce the bulk of the pulp body and obtain a product which is as compact as possible.
It is of great importance for these products that they have a high absorption capacity, that the total absorption capacity is fully utilized, and that the materials included have a good ability to spread the absorbed liquid. The product should also be thin so that it can be used as discreetly as possible.
SE,B,462 622 describes a readily disintegratable product comprising cellulose-containing fibre material, which product is of such a strength that it can be rolled up or handled in sheet form for storage and transportation, without addition of chemicals which increase the bonding strength between the fibres. Flash-dried fibres of a chemithermomechanical pulp, so-called CTMP, with a dry matter content of about 80%, are formed into a web. The fibres are conveyed by an air stream, in a controlled flow, through a forming head arranged over a wire. The air is sucked off through a suction box arranged under the wire. The web is pre-pressed in order to reduce the web bulk prior to the final pressing to a density of 550-1000 kg/m.sup.3. This product is easy to dry-defibre and convert to fluffed form for production of, for example, hygiene articles such as diapers, sanitary towels and similar products. The advantage of the material is that the cellulose pulp in roll form is flash-dried and dry-formed into a web, and the pulp thus has a low content of paper bondings, for which reason the defibering energy is lower than for conventional wet-formed pulp. This also affords possibilities of compressing the material hard, inter alia for reducing the transportation and storage volumes, etc., while retaining the low defibering energy. Another advantage is that superabsorbents can be mixed into the dry-formed material, something which is not possible as regards wet-formed material.
It has been found that this dry-formed material in the non-defibered state is a very good absorption material, and it is possible for the material to be used directly, without defibering, as an absorption material in hygiene articles. This is disclosed in the applications SE 9203445-3 and SE 9203446-1. The material also has good spreading properties and swelling properties. A simpler and less costly production process is achieved, and the conventional defibering and the conventional mat formation are not required. For certain product applications in hygiene articles, it is expedient for dry-formed roll pulp to undergo softening prior to use as absorption material. The good absorption properties and swelling properties already mentioned are not affected to any great extent by the softening process. U.S. Pat. No. 3,938,522 discloses a diaper structure capable of keeping the moisture away from the wearer's skin, which comprises a first layer a porous facing web to be brought into contact with an infant's skin. A second layer, in juxtaposition with the first layer is a highly porous cellulosic batt having greater wettability than the first layer and integral with the second layer is a continuous, paper-like, densified third layer of the same material as the second layer, but of substantially smaller pore size. The third layer is thickened in selected areas providing rapidly drawing away of fluid. A final layer, an impervious sheet, is also provided.
A number of absorbent products, mostly sanitary towels and panty liners which are relatively thin, are nowadays produced using a so-called airlaid material. This material is produced by means of cellulose fibres being airlaid on a wire where they are sprayed with adhesive, for example latex. The airlaid material is thus an adhesive-bonded material. The material is thereafter dried in an oven.
A panty liner consists of a single layer of airlaid material, a lower bottom layer of plastic, for example polyethylene, and an upper surface layer, for example nonwoven. In a sanitary towel the airlaid material is folded into three layers; otherwise, like the panty liner, it consists also of a lower bottom layer made of plastic and an upper surface layer. Other areas of use for the airlaid material are, for example, protective sheets, washing mitts, face cloths, napkins and table cloths.
The previously mentioned dry-formed absorption material is very well suited for use in hygiene products on account of its good absorption properties. In addition, it is without adhesive, which is an advantage from the point of view of cost and the environment. It does, however, have the disadvantage that it is unresilient and brittle and does not hold together so well if the layer of the material is too thin. For producing feminine hygiene products in particular, it is of advantage to have absorption material of narrow web width on a roller or on a spool. In order to supply dry-formed material on narrow rollers (width.apprxeq.5-10 cm) with the strength which is required, the material has to have a grammage of about 350 g/m.sup.2. This grammage is higher than what is in many cases required for the product's function.
The object is the invention is to reduce the grammage of dry-formed absorption material having the strength which is required for it to be supplied on narrow rollers (with.apprxeq.5-10 cm).